The discovery of high temperature superconductive materials in the late 1980's was soon followed by a desire to form such materials into tapes or similar shapes. Ideally such tapes should be physically strong, flexible, highly conductive and able to withstand strong magnetic fields without loss of current carrying capacity.
Processes generally referred to as "powder in a tube" have been developed. For example, a general process of fabricating superconductive tape involves initially preparing a superconductive powder, filling a tube or pipe of silver with the superconductive powder, sealing the pipe or tube, subjecting the pipe or tube to reducing or deforming operations to form tape, and finally sintering the reduced tape at high temperatures.
Efforts to further develop conventional thermomechanical processing methods have been largely unsuccessful in improving the critical current density, J.sub.c, of BSCCO superconducting tapes. Limited current density remains an obstacle in the commercial application of BSCCO high temperature superconductors. Conventional processing involves iterative cycles of mechanical deformation to develop texture and reduce porosity followed by thermal annealing to react components, to relieve stress and to heal microcracks caused by the deformation. Texture and deformation hardening and cracking may limit the ability to obtain the desired grain texture through deformation alone. In addition, the oxide core density of the superconductive tapes decreases during the annealing, causing J.sub.c to decrease as well.
It is an object of the present invention to provide a process of improving critical current density in superconductive tapes by a low pressure compressive annealing of the tapes.
It is a further object of the invention to provide a process of low pressure compressive annealing of superconductive tapes in the absence of tape deformation, i.e., where such low pressure compressive annealing does not subject the tapes to deformation.